Heat accumulating material

ABSTRACT

The heat accumulating material of this invention comprising three components of calcium chloride (CaCl 2 ), urea [CO(NH 2 ) 2  ] and water (H 2  O) can have varied temperatures of heat accumulating and heat releasing between 15° C. and 29.5° C. by varying the proportion of said three components, and also has a large latent heat. Hence, much expectation can be placed on it as a heat accumulating material for air conditioning. Moreover, by adding BaFeO 3-x  (0≦x≦0.53) as a nucleating agent to the above-mentioned composition, supercooling can be greatly decreased and wider application of this heat accumulating material becomes possible.

This invention relates to a heat accumulating material, particularly toa latent heat accumulating material comprising three components ofCaCl₂, CO(NH₂)₂ and H₂ O as its principal ingredients.

Generally, two types of heat accumulating material are known, one typeutilizing the sensible heat of material and the other type making use ofthe latent heat. The heat accumulating material of the type utilizingthe latent heat, as compared with the type utilizing the sensible heat,has the advantage that its heat accumulating capacity per unit weight orunit volume is high, and hence a smaller amount of material is neededfor accumulating a required quantity of heat, allowing a size reductionof the heat accumulator. Also, the heat accumulating material making useof the latent heat has an advantageous property that the temperaturethereof does not decrease with heat dissipation unlike the heataccumulating material of the type utilizing the sensibile heat. Also, itreleases heat of a fixed temperature at the transition point thereof.Especially, the heat accumulating material utilizing the latent heat offusion of an inorganic hydrate is known for its high heat accumulatingcapacity per unit mass and per unit volume.

Now, CaCl₂.6H₂ O (melting point: 29.5° C.) has a high heat accumulatingcapacity and much expectation has been placed on it for its utilizationas a heat accumulating material, such as for air conditioning systems.However, the melting point of CaCl₂.6H₂ O is fixed at 29.5° C., andhence the temperature of heat accumulation and heat releasing isnecessarily restricted to that temperature, and this has been a problemfor its broader application. Also, CaCl₂.6H₂ O has another problem inthat, during the repeated fusion and solidification, CaCl₂.4H₂ Oseparates out, causing gradual decrease of latent heat of the system.

An object of this invention is to provide a heat accumulating materialhaving a high heat accumulating capacity and a stable heat absorbing andreleasing property at a low cost. The temperature for heat accumulationand heat releasing of which material can be controlled by, in acomposition comprising three components of CaCl₂, CO(NH₂)₂ and H₂ O orcomprising these as its principal ingredients, varying the proportion ofsaid composition.

The feature of the heat accumulating material according to the presentinvention consists in comprising three components system of CaCl₂,CO(NH₂)₂ and H₂ O or comprising the system as its principal ingredient.Preferably the material comprises 40-57.5% by weight of CaCl₂, 30% byweight or less (excluding 0%) of CO(NH₂)₂ and 30-52.5% by weight of H₂ O(providing that the total of said three components is 100% by weight).More preferably, the material is of a composition having CaCl₂.6H₂ O andCaCl₂.4CO(NH₂)₂.2H₂ O as its two end components and containing CO(NH₂)₂in a range of amount of 25% by weight or less (excluding 0%) based onthe total amount of CaCl₂, CO(NH₂)₂ and H₂ O.

In order to prevent the supercooling of the composition comprisingCaCl₂, CO(NH₂)₂ and H₂ O, an appropriate nucleating agent such asBaFeO_(3-x) (0≦x≦0.53) is preferably added. The amount of the nucleatingagent to be added is preferably 40 parts by weight or less to 100 partsby weight of the composition comprising CaCl₂, CO(NH₂)₂ and H₂ O.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a DSC (differential scanning calorimeter) diagram obtainedduring the fusion of Sample 7.

FIG. 2 is a graph showing the changes in the degree of supercooling(difference between the solidification temperature and the temperatureat which supercooling is broken) of Sample 54 when it is subjected to1000 consecutive repeated heating and cooling cycles.

The present invention is further described below by way of theembodiments thereof.

EXAMPLE

Commercially available reagent grade CaCl₂, CaCl₂.6H₂ O and CO(NH₂)₂ aswell as water purified by distillation followed by ion exchange wereused to be mixed in prescribed amounts as shown in Tables 1 and 2. Themixture was heated up to 45° C. to dissolve as much solid as possible,and was used as a sample.

Each of these samples was measured for its transition temperature andlatent heat by use of a differential scanning calorimeter (DSC). Thetransition temperature was determined from the temperature at the peakof DSC diagram, and the latent heat was determined from the peak area ofDSC diagram. The DSC diagram of Sample 7 shown in Table 1 is illustratedin FIG. 1. The samples for which two transition temperatures areindicated in Tables 3 and 4 are those having two peaks in DSC diagram,as seen in the above DSC diagram. Actual transition is considered tooccur continuously between these temperatures.

Each of the samples shown in Table 1 is of a composition havingCaCl₂.6H₂ O and CaCl₂.4CO(NH₂)₂.2H₂ O as its two end components, whileeach of the samples shown in Table 2 is of a composition lying inperipheral area of the composition having CaCl₂.6H₂ O andCaCl₂.4CO(NH₂)₂.2H₂ O as its both end components.

Needless to say, transitions below 0° C. were not determined since theywere considered to be unnecessary in this case. Regarding the ratingsshown in Tables 3 and 4, samples having a latent heat not less than 25cal/g were marked with the symbol o, those having a latent heat not lessthan 15 and less than 25 cal/g were marked with the symbol Δ, and theothers were marked with the symbol x. Samples marked with the symbol ohave a high heat accumulating capacity and can be used practically.Samples marked with the symbol Δ are considered to be fairlysatisfactory for practical application since, though their heataccumulating capacity is not so high, they have transition temperaturesin a temperature range not obtainable by prior heat accumulatingmaterials.

                  TABLE 1                                                         ______________________________________                                                 Composition (% by weight)                                            Sample No. CaCl.sub.2  CO(NH.sub.2).sub.2                                                                      H.sub.2 O                                    ______________________________________                                        1          50.6        0.2       49.2                                         2          50.5        0.4       49.1                                         3          50.4        0.6       49.0                                         4          50.3        1.1       48.6                                         5          49.9        2.2       47.9                                         6          49.5        3.2       47.3                                         7          49.1        4.3       46.0                                         8          48.8        5.3       45.9                                         9          47.9        7.9       44.2                                         10         47.4        9.3       43.3                                         11         46.8        10.9      42.3                                         12         46.3        12.4      41.3                                         13         45.7        14.0      40.3                                         14         45.2        15.5      39.3                                         15         44.6        17.1      38.3                                         16         43.8        18.5      37.7                                         17         41.9        24.8      33.3                                         18         41.0        27.0      32.0                                         19         40.2        29.5      30.3                                         20         39.5        31.0      29.5                                         ______________________________________                                    

                  TABLE 2                                                         ______________________________________                                                 Composition (% by weight)                                            Sample No. CaCl.sub.2  CO(NH.sub.2).sub.2                                                                      H.sub.2 O                                    ______________________________________                                        21         45.0        2.5       52.5                                         22         40.0        5.0       55.0                                         23         45.0        5.0       50.0                                         24         47.5        5.0       47.5                                         25         50.0        5.0       45.0                                         26         52.5        5.0       42.5                                         27         55.0        5.0       40.0                                         28         45.0        10.0      45.0                                         29         47.5        10.0      42.5                                         30         50.0        10.0      40.0                                         31         52.5        10.0      37.5                                         32         55.0        10.0      35.0                                         33         57.5        10.0      32.5                                         34         60.0        10.0      30.0                                         35         39.0        15.0      46.0                                         36         45.0        15.0      40.0                                         37         50.0        15.0      35.0                                         38         55.0        15.0      30.0                                         39         42.5        20.0      37.5                                         40         46.0        25.0      29.0                                         ______________________________________                                    

                  TABLE 3                                                         ______________________________________                                                  Tdransition                                                         Sample    temperature  Latnet heat                                            No.       (°C.) (cal/g)   Rating                                       ______________________________________                                        1         29.3         43        o                                            2         29.1         43        o                                            3         28.9         43        o                                            4         28.2         42        o                                            5         27.3         40        o                                            6         26.0, 15.0   39        o                                            7         25.0, 15.1   39        o                                            8         25.0, 16.0   37        o                                            9         24.0, 16.3   37        o                                            10        22.3, 16.8   35        o                                            11        20.8, 17.3   34        o                                            12        18.1         33        o                                            13        18.1         34        o                                            14        15.8         32        o                                            15        14.1, 0.8    28        o                                            16        14.0, 1.0    26        o                                            17        14.0, 1.6    25        o                                            18        13.2, 1.6    23        Δ                                      19        13.0, 1.7    18        Δ                                      20        13.0, 1.8    12        x                                            ______________________________________                                    

                  TABLE 4                                                         ______________________________________                                                  Transition                                                          Sample    temperature                                                         No.       (°C.) Latent heat                                                                             Rating                                       ______________________________________                                        21        19.5         17        Δ                                      22         4.0         10        x                                            23        19.6         20        Δ                                      24        23.0         25        o                                            25        24.0         37        o                                            26        27.0         36        o                                            27        33.6, 20.0   35        o                                            28        10.3         21        Δ                                      29        20.8, 17.0   38        o                                            30        20.9, 18.3   37        o                                            31        21.3         36        o                                            32        32.6, 18.3   33        o                                            33        32.6, 19.0   25        o                                            34        33.3, 19.3   14        x                                            35         4.3          7        x                                            36        16.3         31        o                                            37        19.6         33        o                                            38        33.0, 20.3   24        o                                            39        16.0, 2.5    21        Δ                                      40        13.0, 1.8    10        x                                            ______________________________________                                    

When the data shown in Table 3 are examined, in Sample 1, which is ofthe composition having CaCl₂.6H₂ O and CaCl₂.4CO(NH₂)₂.2H₂ O as the twoend components and contains 0.2% by weight of CO(NH₂)₂, the transitionpoint lowers to 29.3° C. and the latent heat is 43 cal/g, approximatelyequal to that of CaCl₂.6H₂ O. As the content of CO(NH₂)₂ is increased,the transition point goes down gradually, accompanied by, though slight,a decrease of the latent heat. When the content of CO(NH₂)₂ is 3.2% byweight or more, a transition point appears around 15° C. aside fromprevious transition point of around 26° C. As the content of CO(NH₂)₂increases further; the transition at around 26° C. shifts to the lowertemperature side.

In Sample 12, which contains 12.4% by weight of CO(NH₂)₂, thetransitions at higher and lower temperature sides are observed in anoverlapped state. Accordingly, the composition which contains about12.4-15.5% by weight of CO(NH₂)₂ and has CaCl₂.6H₂ O andCaCl₂.4CO(NH₂)₂.2H₂ O as its two end components, such as Samples 12, 13and 14, is an excellent heat accumulating material having a transitionpoint at 15°-18° C. and a large latent heat of 35 cal/g.

In samples containing 17.1% by weight or more of CO(NH₂)₂, thetransition appears around 1° C. in the further lower temperature side.As the content of CO(NH₂)₂ is increased, the latent heat decreases,while the transition around 15° C. shifting toward the lower temperatureside and the transition around 1° C. shifting somewhat toward the highertemperature side.

In sum, the heat accumulating material of three components system ofCaCl₂, CO(NH₂)₂ and H₂ O, which has CaCl₂.6H₂ O and CaCl₂.4CO(NH₂)₂.2H₂O as its two end components and contains CO(NH₂)₂ in a range of amountof 25% by weight or less (excluding 0%), is a very excellent heataccumulating material unobtainable hitherto, because the heataccumulating and heat releasing temperature can be controlled by varyingthe percentage composition thereof and yet the material has a latentheat of not less than 25 cal/g.

In the next place, samples shown in Table 4, whose composition lies inthe peripherial area of the composition having CaCl₂.6H₂ O andCaCl₂.4CO(NH₂)₂.2H₂ O as its two end components, are examined for theircharacteristic properties. Samples 22-27, as apparent from Table 2, areobtained by varying the proportion of CaCl₂ and H₂ O contained whilekeeping the content of CO(NH₂)₂ at a constant value of 5% by weight.Samples 22, 23 and 24 are those which have their composition in the H₂ Oexcess side, that is, the CaCl₂ deficiency side, of the compositionhaving CaCl₂.6H₂ O and CaCl₂.4CO(NH₂)₂.2H₂ O as its two end components,while Samples 25, 26 and 27 are inversely those which have theircomposition in the H₂ O deficiency side, that is, the CaCl₂ excess side,of the composition having CaCl₂.6H₂ O and CaCl₂.4CO(NH₂)₂.2H₂ O as itsboth end components. Accordingly, as the content of CaCl₂ is increasedstarting from the composition of Sample 22 lying in the H₂ O excess sidewithout varying the content of CO(NH₂)₂, namely, as the composition isvaried into that of Sample 23 and further into that of Sample 24, thelatent heat increases and the transition temperature rises.

In Sample 25, which has the composition nearest to the one havingCaCl₂.6H₂ O and CaCl₂.4CO(NH₂)₂.2H₂ O as its two end components, thelatent heat assumes a maximum value. On increasing the CaCl₂ contentfurther, there is observed not an increase but a decrease of the latentheat. The transition temperature rises with increasing CaCl₂ contentwithout showing any maximum value in the course. Such a relationship canalso be observed among the samples containing 10% by weight of CO(NH₂)₂,such as Samples 28-34. It is observed that Sample 29, which has thecomposition nearest to the composition having CaCl₂.6H₂ O andCaCl₂.4CO(NH₂)₂.2H₂ O as its both end components, has the largest latentheat and that the transition point rises with the increase of thecontent of CaCl₂.

In other words, when compared with the composition having CaCl₂.6H₂ Oand CaCl₂.4CO(NH₂)₂.2H₂ O as its two end components, if the proportionof the CO(NH₂)₂ contained is the same, the transition temperature lowerson the H₂ O excess side, namely the CaCl₂ deficiency side, andinversely, the transition temperature rises somewhat on the H₂ Odeficiency side, namely the CaCl₂ excess side. The latent heat decreasesin both cases when the composition shifts toward the H₂ O excess side,namely CaCl₂ deficiency side, and toward the H₂ O deficiency side,namely CaCl₂ excess side, from the composition having CaCl₂.6H₂ O andCaCl₂.4CO(NH₂)₂.2H₂ O as its two end components.

To sum up the results mentioned above, the composition of a heataccumulating material is preferably in the composition area of Samplesmarked with the symbols of Δ and o shown under the ratings in Tables 3and 4. In other words, in the three components system comprising CaCl₂,CO(NH₂)₂ and H₂ O, it is preferably in the range of 40-57.5% by weightof CaCl₂, 30% by weight or less (excluding 0%) of CO(NH₂)₂ and 30-52.5%by weight of H₂ O. More preferably, the material is of the compositionhaving CaCl₂.6H₂ O and CaCl₂.4CO(NH₂)₂.2H₂ O as its two end componentsand contains 25% by weight or less (excluding 0%) of CO(NH₂)₂ based onthe total amount of CaCl₂, CO(NH₂)₂ and H₂ O.

When a composition comprising CaCl₂, CO(NH₂)₂ and H₂ O is employed as aheat accumulating material, an appropriate nucleating agent ispreferably used for the purpose of decreasing supercooling. It was foundthat BaFeO_(3-x) (0≦x≦0.53) acts as said nucleating agent for saidcomposition. Since BaFeO_(3-x) (0≦x≦0.53) is a substance of limitedsolubility in water, it exhibits a nucleating effect in an amount ofabout 0.01 parts by weight based on 100 parts by weight of saidcomposition. Of course it may also be used in larger amounts.

In use of the heat accumulating material of this invention as a heataccumulator for air conditioners and the like, said material is usuallyused in an amount of about 100 to 1000 kg. In this case, even if thecomposition comprising CaCl₂, CO(NH₂)₂ and H₂ O is fused down, the wholesystem would not become a uniform composition, and a solution with a lowCaCl₂ concentration would exist in the upper portion while theprecipitate of the nucleating agent and a high concentration solution ofCaCl₂ and the nucleating agent would stay in the lower portion.Therefore, even if the amount of the nucleating agent added in thecomposition is far less than the minimum amount which would be requiredwhen the whole system forms a uniform solution, said nucleating agentwould not dissolve completely, and would retain and perform its dueaction. The minimum amount of the nucleating agent necessary for formingthe crystal nuclei, that is, the lower limit of the amount to be mixed,depends, accordingly, on the amount and constitution of the compositionemployed as well as the size and form of the container which holds theaccumulating material. Thus, the amount of the nucleating agent to beactually used needs to be chosen according to the conditions of use.

However, addition of the nucleating agent in a too great amount leads toa substantial reduction of heat accumulating capacity of the heataccumulating material as a whole. For practical use, therefore, it isdesirable that the nucleating agent is blended in an amount notexceeding 40 parts by weight to 100 parts by weight of the compositioncomprising CaCl₂, CO(NH₂)₂ and H₂ O.

The BeFeO_(3-x) used as the nucleating agent was obtained by mixingBaCO₃ or Ba(NO₃)₂ with Fe₂ O₃ in a molar ratio of 1:1 and then burningthe mixture in an oxygen gas atmosphere. The value of x was determinedby chemical analysis.

This invention is further illustrated with reference to Example. Thecompositions of samples used in Example are shown in Table 5.

                  TABLE 5                                                         ______________________________________                                                           Nucleating agent                                           Sample                                                                              Composition (% by weight)    Amount                                     No.   CaCl.sub.2                                                                             CO(NH).sub.2).sub.2                                                                     H.sub.2 O                                                                           BaFeO.sub.3-x                                                                         added (g)                              ______________________________________                                        51    50.3     1.1       48.6  BaFeO.sub.2.47                                                                        0.01                                   52    50.3     1.1       48.6  BaFeO.sub.2.74                                                                        0.01                                   53    50.3     1.1       48.6  BaFeO.sub.3.00                                                                        0.01                                   54    50.3     1.1       48.6  BaFeO.sub.2.74                                                                        1.0                                    55    50.3     1.1       48.6  BaFeO.sub.2.74                                                                        40.0                                   56    50.5     0.4       49.1  BaFeO.sub.2.74                                                                        1.0                                    57    49.9     2.2       47.9  BaFeO.sub.2.74                                                                        1.0                                    58    48.8     5.3       45.9  BaFeO.sub.2.74                                                                        1.0                                    59    46.3     12.4      41.3  BaFeO.sub.2.74                                                                        1.0                                    60    45.2     15.5      39.3  BaFeO.sub.2.74                                                                        1.0                                    ______________________________________                                    

The amount added of the nucleating agent indicated in Table 5 is basedon 100 g of the composition comprising CaCl₂, CO(NH₂)₂ and H₂ O.

Eight hundred grams of each of Samples 41 to 50 was placed respectivelyin a cylindrical vessel measuring 100 mm in inner diameter and 100 mm inheight, and the vessel was tightly closed by a plug having athermocouple insert tube. The vessel was then subjected to repeatedheating and cooling between 0° C. and 35° C. In every case, thesupercooling broke in a temperature range 2° C. to 4° C. below thesolidification temperature, no deposition of CaCl₂.4H₂ O was observed,and fusion and solidification could be repeated in a stable state. Whena sample of CaCl₂.6H₂ O to which a small amount of BaFeO₂.74 had beenadded was subjected to repeated heating and cooling under the sameconditions, though the supercooling was broken satisfactorily, CaCl₂.4H₂O separated out and the latent heat of the sample decreased gradually.

FIG. 2 shows the changes of the degree of supercooling (differencebetween the solidification temperature and the temperature at whichsupercooling is broken) observed when Sample 54 was subjected to 1000consecutive repeated heating and cooling cycles.

All of these samples had a latent heat of 25 cal/g or more and had asufficient heat accumulating capacity for use as a heat accumulatingmaterial.

From the foregoing, it was confirmed that the heat accumulating materialof this Example has a stable heat absorbing and heat releasing propertyand no problem is encountered even in continuous use.

As described above, the heat accumulating material of this inventioncomprises three components of CaCl₂, CO(NH₂)₂ and H₂ O or comprisesthese as its principal ingredients, the heat accumulating and heatreleasing temperature of said material can be controlled by varying theproportion of these three components, and moreover, supercooling of saidmaterial can be decreased by employing a nucleating agent such asBaFeO_(3-x) (0≦x≦0.53), and the material has a very stable heatabsorbing and heat releasing property as well as a high heataccumulating capacity.

It is needless to say that, in the present invention, other fusing pointdepresser may be jointly used, other nucleating agent may be used, athickening agent for preventing sedimentation or aggregation of thenucleating agent may be used, and other additives may be optionallyincorporated. The heat accumulating material of this invention can beused not only for a heat accumulator of an air conditioner for roomcooling and heating purpose, but for all fields of applicationsutilizing heat accumulation.

What is claimed is:
 1. A heat accumulating material characterized inthat CaCl₂, CO(NH₂)₂ and H₂ O are present in a composition of 40-57.5%by weight of CaCl₂, 30% by weight or less (excluding 0%) of CO(NH₂)₂ and30-52.5% by weight of H₂ O.
 2. The heat accumulating material accordingto claim 1, characterized in that CaCl₂, CO(NH₂)₂ and H₂ O are presentin a composition having CaCl₂.6H₂ O and CaCl₂.4CO(NH₂)2.2H₂ O as its twoend components and containing 25% by weight or less (excluding 0%) ofCO(NH₂)₂.
 3. A heat accumulating material according to claim 1,characterized in that BaFeO_(3-x) (0≦x≦0.53) is added to a compositioncomprising CaCl₂, CO(NH₂)₂ and H₂ O.
 4. The heat accumulating materialaccording to claim 3, characterized in that the BaFeO_(3-x) (0≦x≦0.53)is added in a range of 40 parts by weight or less (excluding 0 parts) to100 parts by weight of the composition comprising CaCl₂, CO(NH₂)2 and H₂O.